The present invention relates to a seal assembly for sealing a clearance space between first and second displacable cylindrical surfaces, and more particularly to a seal assembly which includes mechanically inter-locked anti-extrusion rings located adjacent to at least one side of the seal.
The use of seal assemblies which include a T-shaped sealing ring and a pair of back up or anti-extrusion rings to form a seal between two relatively displacable cylindrical surfaces is generally known. Such assemblies are often used in hydraulic or pneumatic systems, in both rod in bore and piston in cylinder seal applications. T-shaped seal assemblies provide a significant performance advantage over the previously known O-ring seal configurations.
In one known seal arrangement described in U.S. Pat. No. 5,524,905, which is assigned to the assignee of the present invention and incorporated herein by reference as if fully set forth, a T-shaped seal ring with two anti-extrusion rings is provided. The anti-extrusion rings prevent the seal from extruding into the gap between the cylindrical surfaces being sealed. In one embodiment, the anti-extrusion rings are provided in two pieces. An inboard ring is provided which contacts the upstanding portion of the seal and an outboard ring is located between the inboard ring and the wall of the groove. The inboard ring is made of a softer, resilient material in order to avoid abrasive wear to the upstanding seal leg. The outboard back-up ring is preferably made of a harder material and prevents abrasion of the inner ring on the groove wall and extrusion of the inner ring in the clearance space. However, the known anti-extrusion rings of this type sometimes create problems during installation. This concern is primarily due to the number of pieces needed to be installed.
In another known seal arrangement described in U.S. Pat. No. 3,188,099, interconnected back-up rings are provided for a seal. An inner back-up ring is provided with a groove, and a rib is provided on the outer back-up ring which can be a dovetail fit with the groove. However, the rib and groove have angular corners which increase stress concentrations in the back-up rings at the juncture.
It is also known to use anti-extrusion rings with cap seals. Cap seals generally consist of an elastomer energized seal located in a groove, with the elastomer energizer pressing the seal member against the mating surface. Anti-extrusion rings are provided on each side of the seal member and the energizer, adjacent to each of the groove side walls, in order to prevent abrasion and extrusion of the seal and the energizer. In one known cap seal, described in U.S. Pat. No. 4,576,386, the anti-extrusion rings are made of inner and outer elements. The outer element is made from a relatively hard, non-resilient material which is sufficiently strong to prevent extrusion of the cap seal. The inner member is made of a relatively soft plastic material which does not abrade or chafe the soft elastomer energizer. The outer member and inner member are provided as single pieces which matingly position the outer member adjacent to the inner member. However, the pieces must be formed as complete rings or be bonded together in order to maintain the outer member in position. This limits the installation options.
It would be desirable to provide a two-piece backup ring to protect against extrusion of a seal member at high pressure or vacuum, which also protects the seal member from excessive abrasion. Ideally such a seal would provide the option of being closed around a fixed shaft and desirably have a fool proof assembly arrangement to assure proper alignment of the soft and the hard back-up rings. Preferably, such back-up rings can be machined or formed from strips of material to a specific size as appropriate for a given application.